Flow responsive switch apparatus
BACKGROUND OF THE INVENTION 
     This invention relates generally to flow responsive switch apparatus, and more particularly to improved apparatus of this type wherein the flow responsive arm is supported to minimize fatigue failure. 
     In prior flow switch devices, a cantilevered arm was deflected in bending by the flow into unsupported position in the flow stream, whereby the arm was then subject to back and forth bending in the flow stream in response to varied flow conditions such as turbulence. This often led to early fatigue failure of the arm, and required frequent arm replacement. 
     Accordingly, there is need for an improved device not subject to such early fatigue problems. There is also need for improved flow switch apparatus which is very simple, easily downsized, highly reliable, and which can be installed and operated in pipes or ducts extending at different angles. 
     SUMMARY OF THE INVENTION 
     It is a major object of the invention to provide an improved fluid flow responsive switch which meets the above needs. As will be seen, the apparatus of the invention is installable into ducting or piping wherein fluid, such as liquid, flows forwardly, the apparatus comprising: 
     a) a support body connectible to said ducting, 
     b) a stem carried by the body to project therefrom into a liquid flow zone in the ducting, and magnetically responsive switch means in the stem, 
     c) a cantilevered arm carried by the body to project into said flow zone upstream of said stem and to be deflected downstream into supported relation with the stem in response to flow impingement on the arm, 
     d) and magnetic means carried by the arm to be displaced by said stem deflection into sufficiently close proximity with the stem and said switch means as to effect switch operation. Typically, the arm has a substantially flat surface facing upstream away from the stem to receive direct flow impingement thereagainst; and the arm has a first position spaced from said stem and toward which it is yieldably urged in the absence of said flow, the arm having a second position when flow deflected into said supported relation with the stem. 
     It is another object of the invention to provide the arm in the form of a flat spring which is yieldably bent in said second position; also, the arm has a supported end in a hollow formed by the body out of the main flow stream, the arm tapering in width away from its supported end, and in the flow stream. Further, the arm has a large lower end extent responsive to the flow, and forming an opening for retention of magnet encapsulating cup parts positioned to be deflected squarely toward and against the switch stem, for switch actuation and arm support, in response to the flow impingement upon the arm. 
     These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which: 
    
    
     DRAWING DESCRIPTION 
     FIG. 1 is a section taken in elevation, showing one form of the invention; 
     FIG. 2 is a fragmentary view showing a portion of the stem, cantilevered arm, and magnetic means as the arm, deflected by water flow into switch actuating position; 
     FIG. 3 is a top plan view taken on lines 3--3 of FIG. 1; 
     FIG. 4 is a plan view of a cantilevered arm; 
     FIG. 5 is an enlarged section, showing arm support of a magnet and magnet holder; 
     FIG. 6 is a fragmentary section taken in elevation, showing mounting of one end of the cantilevered arm; 
     FIG. 7 is a section showing a reed switch in the stem, and its proximity to the magnet, in arm deflected position; and 
     FIGS. 8, 9 and 10 are views that show the construction of the upper portion of the arm and stem supporting body. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows the liquid flow switch apparatus 10 connected into ducting 11 wherein liquid flows forwardly, as indicated by arrows 12. The apparatus 10 includes a support body 13 having exterior threading 14 that is received into interior threading 15 in a hollow tee section 16 of the ducting. The tee and ducting may consist of synthetic resin, as may the support body 13. A cap 17 on the body carries a cable 18 from which electrical wires project at 19a and 19b. 
     A stem 20 is carried by the body to project downwardly into a liquid flow zone 21 in the ducting 11, as shown. The stem may be integral with the body 13, and is typically hollow at 20a to receive a magnetically responsive switch 22. See FIGS. 2 and 7. The switch may be encapsulated in the stem, as indicated by encapsulating epoxy resin seen at 23 in FIG. 7. The switch extends close to frontward facing wall 20b of the stem for magnetic actuation by a permanent magnet 23 in an encapsulating structure 24. 
     A cantilevered arm 25 is also carried by the body 13 to project downwardly into the flow zone 21, but upstream of the stem 20. See the flow direction arrows 12, in FIG. 1. The arm is supported to be deflected downstream into supported relation with the stem in response to flow impingement upon arm extent projecting into the flow zone. The arm has a flat, enlarged lower portion 25a facing the flow, for quick response to the flow, and an upper portion 25b that tapers toward portion 25a for aiding bending deflection into the position as seen in FIG. 2. Such taper also minimizes bending stress. Note also that the arm is bent at 25c between portions 25a and 25b, so that arm portion 25a squarely approaches the stem as seen at 25a&#39; in FIG. 1. This facilitates square approach of structure 24, i.e. to flatly engage the stem, at 125 seen in FIG. 2. 
     The uppermost extent 25d of the metallic arm 25 is fixedly supported by the body 13, as within a hollow 30, above the flow zone, and within tee section 16. FIG. 6 shows one highly advantageous method of attaching the arm to interior wall 16a of the tee section. As seen, the arm portion 25d is bent approximately 90°, and retained flatly against wall 16a, as by a fastener or fasteners 32 and/or by potting resin 33, such as epoxide, filled into hollow 30 to the depth shown. This establishes vertical support for the arm upper portion 25b, such to facilitate arm bending to the position as seen at 25&#39; in FIGS. 2. 
     It is an important feature that, with the structure 24 engaging the stem, the arm is held in fixed position by flow impingement on the arm, minimizing arm oscillation that could otherwise lead to early fatigue failure. 
     FIGS. 4 and 5 illustrate the provision of an opening 76 in the arm lower portion 25a, for reception of skirt 38a of a plastic cup 38, the cup head 38b engaging the side 25f of the arm. A second plastic cup 39 has a skirt 39a that telescopically interfits skirt 38a; also rim 39b of the skirt 39a engages the side 25g of the arm, to position the two cup elements for reception and retention of a permanent magnet 23 therein, as shown. When bonded together, the two skirts firmly hold the structure 24 to the arm, with the magnet positioned therein, for actuation of the switch. 
     FIG. 7 shows the switch 22 in the form of a &#34;reed&#34; switch, to be actuated by the magnet wherein the structure 24 is in full line position as shown. Switch wires 46 and 47 extend upwardly within the stem for suitable connection with the ends of wires 18 and 19, within cap 17. 
     If desired, the apparatus may be rotated so as to extend at about 90° to the position shown, whereby stem 20 and arm 25 then extend generally horizontally. Also, the device may be inverted, and may be used in pipes extending at various angles. 
     The simplicity of the device, as described, permits small size and low profile application. 
     Note in FIGS. 1, 8 and 10, the provision of two support arms 60 and 61 integral with body 13, and projecting downwardly. They provide stop shoulders 60a and 61a to be positively or forcibly engaged by the arm upper extent 25b in the hollow 30, in the absence of flow, due to the spring characteristics of the flat spring arm. Thus, the arm is normally in one or the other of two stable positions (engaging 60 and 61 in arm &#34;relaxed&#34; position, and engaging the stem 20 in flow deflected arm position) to minimize arm bending, and optimize fatigue strength. 
     The switch apparatus is useful in flow streams consisting of either liquid or gas. Also, the body, and/or stem, and/or ducting may consist of plastic or metal, or other suitable material.